A mobile terminal such as a cellular phone, for example, is designed using a plurality of system devices. Many of such system devices included in the mobile terminal incorporate a data communication function and require a plurality of different voltages. As such, the mobile terminal uses a multiple power supply device which has a regulator and a converter for generating various voltages necessary for the plurality of system devices in one package, and supplies the voltage necessary for each system device from the multiple power supply device.
FIG. 10 is a block diagram illustrating a schematic constitution of the mobile terminal using a conventional multiple power supply device. This mobile terminal is provided with a battery 100, a power device 101 such as a power amplifier, a multiple power supply device 102, and an MPU (microprocessor unit) 103 and a first device (device 1) 104 to a fifth device (device 5) 108 as the plurality of system devices. The MPU 103, the first device 104 and the second device 105 are interconnected via an interface (I/F1) 111 to perform data communication. The MPU 103, the third device 106 and the fourth device 107 are interconnected via an interface (I/F2) 112 to perform data communication. The MPU 103 and the fifth device 108 are interconnected via an interface (I/F3) 113 to perform data communication.
In the mobile terminal shown in FIG. 10, a battery voltage of the battery 100 is directly supplied to the power device 101, whereas the battery voltage of the battery 100 is dropped or raised to a predetermined voltage by the multiple power supply device 102 before supplied to the MPU 103 and the first device 104 to the fifth device 108.
Therefore, in order to supply power to respective system devices and interfaces, the multiple power supply device 102 is provided with a power supply circuit (MPUReg) 121 for an MPU core of the MPU 103, a power supply circuit (1/F1Reg) 122 for the interface 111, a power supply circuit (1/F2Reg) 123 for the interface 112, a power supply circuit (1/F3Reg) 124 for the interface 113, a power supply circuit (IC1Reg) 125 for an IC core of the first device 104, a power supply circuit (IC2Reg) 126 for an IC core of the second device 105, a power supply circuit (IC3Reg) 127 for an IC core of the third device 106, a power supply circuit (IC4Reg) 128 for an IC core of the fourth device 107, and a power supply circuit (IC5Reg) 129 for an IC core of the fifth device 108. The multiple power supply device 102 is controlled by the MPU 103 via an interface (I/F0) 110.
The multiple power supply device shown in FIG. 10 is used not only for the mobile terminal but also for other electronic devices. The multiple power supply device is used for the electronic device because it can reduce a mounting area and therefore contribute to downsizing of the device by incorporating power supply circuits necessary to generate power for respective system devices and a power supply circuit having a regulator and a convertor common to the system devices within a single package.
In addition, when it is used for a small device such as the mobile terminal in particular, a substrate to be used can be designed to be small enough and a power supply line from the multiple power supply device to each system device can be short. Since the line impedance may thereby be reduced, it is possible to limit the voltage drop within an allowable range relatively easily.
In a case where the voltage drop cannot fall within the allowable range, a countermeasure which has been taken is, in case of a low voltage power supply, to detect a voltage for feedback from an input power supply terminal of the system device and, by using the voltage for feedback, to control a voltage at a corresponding output terminal of the multiple power supply device to be increased such that the voltage at the input power supply terminal of the system device is at a predetermined level.
However, in recent small devices, system devices which are miniaturized and perform at a high speed as well as being capable of performing large current at low voltage are used. When such a system device is used, since the voltage drop has influence even if the power supply line is short because of large current at low voltage, and a difference between the maximum operation power and the minimum operation power is large because of low power operation, it is not possible to follow the voltage drop by output setting for increasing the voltage. It may also not be able to follow to a transient response because of the high speed when output voltage is controlled by detecting a feedback voltage.
There may be a method to reduce the voltage drop by designing the power supply line (pattern) to be thick to minimize the line impedance. However, the thick pattern increases the size of substrate, thereby preventing downsizing.
In addition, the multiple power supply system which supplies power using the multiple power supply device stated above needs to redesign the power supply if the system is expanded exceeding a limit for power designing because of addition of functions to the device.
On the other hand, there is known a dispersed power supply system (Point-of-Load) other than the multiple supply system described above as the power supply system for the system devices. The system arranges a power supply circuit having a regulator and a convertor close to each system device and forms shortest connection between the power supply circuit and a corresponding system device to supply power.
Since the power supply circuit is connected to each system device by the shortest connection in the dispersed power supply system, it may not cause a problem such as the voltage drop and may easily allow the device to incorporate additional functions by changing the battery capacity, for example. However, in the dispersed power supply system the power supply circuits are arranged dispersedly corresponding to the system devices, resulting in increase of the number of components and thus increase of the mounting dimension. For this reason, the dispersed power supply system has been hardly used for small devices such as the mobile terminal.
However, there is recently suggested a hybrid device, as a device for the dispersed power supply system, which is a hybrid IC mounting power supply circuits individually in a package size of a conventional device or smaller. Accordingly, such hybrid device of the dispersed power supply system can solve both issues of downsizing and low voltage performance.
Nonetheless, in the dispersed power supply system, as shown in FIG. 10 for example, the voltage of the interface 111 which interconnects the MPU 103, the first device 104 and the second device 105 for data communication is generated at each device of the MPU 103, the first device 104 and the second device 105. Therefore, in comparison to the multiple power supply system which supplies power by generating the voltage of the interface 111 with a single power supply circuit (I/F1Reg) 122 commonly provided to the multiple power supply device 102, power supply circuits are overlapped and, the more overlapped they are, the more self-power-loss is generated at voltage conversion.
In addition, when the voltage for the interface is generated at each device connected via the interface, it is difficult to generate the same voltage, because of difference in individual power supply circuits. Therefore, it is concerned that some interfaces would not operate because of voltage difference between the devices and that malfunction may be caused because of detecting a false value, reducing reliability of performance.
As a power supply circuit which reduces self-power-loss, there is known a power supply circuit to be turned on/off based on an output voltage of a main battery (for example, see Patent Document 1).
However, the power supply circuit disclosed in Patent Document 1, if the output voltage of the main battery is equal to or higher than a predetermined value when a system is off, performs backup of a memory device by turning the power supply circuit off and directly supplying the output voltage of the main battery to the memory device of the system. While the system is on by external power supply (from another power supply circuit), the power supply circuit is never turned off. Therefore, it cannot reduce self-power-loss.
Patent Document 1: Japanese Patent Application Laid-Open No. 10-301673